JPH0675051A - Imaging device - Google Patents

Abstract

PURPOSE:To enhance image quality even in a high count region by dividing the capacity value of a pulse counter, when overflow takes place during sampling, by the sampling time upto the overflow thereby determining an image data. CONSTITUTION:A sensor 3 counts photons in an incident X-ray and produces a pulse which is inputted through an amplifier 4 to a counter 1. A counter 2 counts output pulses from an oscillator 6 thus measuring the sampling time. Both counters 1, 2 are 8 bit counters and overflow at the count of 128. The counters 1, 2 are actuated by a command delivered from a CPU 8 and outputs from the counters 1, 2 are fed to an operating circuit 7. If the counter 1 does not overflow during sampling, the circuit 7 transfers the count of the counter 1 to the CPU 8 where logarithmic value thereof is determined. In case of overflow, count of the counter 2 minus one is subtracted from the least significant 7 bits of the count of the counter 1 and the difference is transferred to the CPU 8 where the count of the counter 1 is divided by the count of the counter 2 and the logarithmic value of qoutient is determined. Thus determined value is delivered, as an image data, to an image display 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for picking up a radiation image such as an X-ray image, and more particularly to a so-called photon counting system for obtaining a grayscale image by counting radiation photons incident on a solid-state sensor. Regarding the equipment

[0002]

2. Description of the Related Art Conventionally, in this type of image pickup apparatus, generally, C
By scanning an array sensor using a compound semiconductor such as dTe, the X-ray dose at each position is counted and an image is obtained in which the dose count value at each position is the pixel density. Since there is a property that the dose decreases exponentially while passing through a subject, conventionally,
Image data was obtained by simply counting the transmitted X-ray dose with a counter and then taking the logarithm of the count value.

[0003]

By the way, when the logarithmic calculation of the count value of the X-ray dose is performed, for example, as shown in the table below, there is no problem in the low count region, but the high count region Then, there is a problem that the difference in the calculation result becomes small and the quality of the image on the high count side is deteriorated.

[0004]

[Table 1]

The present invention has been made in order to solve the above-mentioned conventional problems, and its purpose is to basically adopt a photon counting system and to provide an image even in a high count side. It is to provide an image pickup device having high quality.

[0006]

A structure for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. In the image pickup apparatus of the present invention, pulsed electric power is generated by incidence of radiation photons. A radiation sensor 3 that generates a signal, a counter (first counter) 1 that counts an electrical signal from the sensor 3, and when the count value of the counter 1 is over capacity during sampling of image data, Clocking means (for example, the oscillator 6 and the second counter 2) for measuring the data sampling time until the capacity becomes over, and arithmetic processing means (for example, the arithmetic circuit 7 and the CPU)
8). When the counter 1 does not become over capacity during data sampling, the arithmetic processing means obtains image data from the count value,
When the capacity is exceeded, the counter 1
It is characterized in that the image data is obtained from a value obtained by dividing the capacitance value of No. 1 by the time measured by the above-mentioned time measuring means, and the data is output on the screen.

[0007]

[Function] Counter 1 is over capacity (overflow)
If not, the count value of the counter 1 is used as it is. However, when overflow occurs, the value obtained by dividing the count capacity value of the counter 1 by the time required for overflow is used as the count value. The data becomes large.

For example, if the counting capacity value of the counter 1 is 128,
If the sampling time is 128 μsec, the time required for overflow to occur is (127/128), (64/128), (5 /
128) μsec, the count values are 12
It becomes 9,256,3268.8, and the data on the high count value side becomes large.

[0009]

1 is a block diagram showing a circuit configuration of an embodiment of the present invention. The sensor 3 generates a pulsed electric signal according to the number of photons of the incident X-ray. The output signal of the sensor 3 is amplified by the amplifier 4, and further the comparator 5
After the wave height is selected by (1), it is guided to the first counter 1.

The first counter 1 is an 8-bit counter. When the count value reaches 128, the highest value bit becomes "1", and the highest value bit is provided as an overflow flag.

On the other hand, the second counter 2 counts pulse signals from the oscillator 6 having an oscillation frequency of 1 MHz.
The count value is used as a time value for sampling the image data. This second counter 2 is also an 8-bit counter, and when the count value reaches 128, the most significant bit becomes "1", and the count value at that time, that is, 128 µsec, is the sampling time of this imaging device once. Is defined as

The above two counters 1 and 2 are CP
Counting is started at the same time by the command of U8, and each output is guided to the arithmetic circuit 7. The arithmetic circuit 7 transfers the counter value of the first counter 1 to the CPU 8 as it is when the first counter 1 is not flagged during data sampling. On the other hand, when the flag is set in the first counter 1 within the data sampling time (128 μsec), “1” is subtracted from the count value of the second counter 2 in the lower 7 bits excluding the most significant bit. The value is entered and transferred to the CPU 8. In addition, like this,
Transferring the value minus "1" depends on the sampling time
When the count value of the first counter 1 reaches 128 at the same time when it reaches 128 μsec, the highest value bit of the two counters 1 and 2 are both set to “1”, preventing the operation from becoming inoperable. This is because

Then, the CPU 8 performs an operation described later on the basis of the transferred data to create image data, and outputs the image data to the image display 9. Next, specific numerical examples of data will be described with reference to Table 2 below.

[0014]

[Table 2]

First, when the first counter 1 does not overflow during data sampling, the most significant bit of the first counter 1 is "0" as shown in the table.
Then, the most significant bit of the second counter 2 becomes "1", the data "00010000" (count value 16) of the first counter 1 is transferred to the CPU 8 as it is, and its logarithmic value 1.20 is obtained. .

On the other hand, the data sampling time (128 μse
If an overflow occurs within c), the most significant bit of the first counter 1 is "1" as shown in the table.
And the data of the second counter 2 at this point is “0000
The data "10000011" incorporating the data obtained by subtracting "1" from "0100" is transferred to the CPU 8, and the count value and the logarithmic value thereof by the following division are obtained.

That is, when the first counter 1 overflows, the capacity count value "128" of the first counter 1 is changed to the time count value of the second counter 2: T = (1 /
128) [μsec / count.] × (4) [count.] Is used for the calculation. In this example, 128 / T = (128 × 128) / 4 = 4096, which is after logarithmic calculation. The value will be “3.61”.

Next, in order to make the above embodiment more detailed, examples of calculated values of image data from the low count region to the high count region are shown in the following table.

[0019]

[Table 3]

As is clear from Table 3, the difference between the respective data is that the data on the high count side is larger than the data on the low count side. Therefore, in the embodiment of the present invention,
It is possible to obtain an image in which the shading of the region on the high count side is particularly emphasized.

In the above embodiments, the 8-bit counter is used, but the number of bits is not limited to this, and may be any number depending on the radiation dose to be detected and the data sampling time. Set to. Further, as the sampling time measuring means, other equivalent alternative means such as a known general timer may be used instead of the configuration shown in FIG.

[0022]

As described above, according to the present invention,
A counter that counts the pulse signals from the radiation sensor,
When an overflow occurs during data sampling, the value obtained by dividing the counter's capacitance value is used for image data in the time required for the overflow, so in the photon counting method, the level in the high count side area is used. The tone can be deepened, and an X-ray image of higher quality than before can be obtained.

Incidentally, in the past, the detection limit on the high dose side such as X-rays was defined by the capacity of the counter, but according to the image pickup apparatus of the present invention, the detection limit is not defined by the capacity of the counter, so it is dynamic. It is also possible to achieve the effect that the range can be set wider than in the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

[Explanation of symbols]

 1 ... 1st counter 2 ... 2nd counter 3 ... Sensor 6 ... Oscillator 7 ... Arithmetic circuit 8 ... CPU 9 ... Image display apparatus

Claims (1)

[Claims] 1. A radiation sensor that generates a pulsed electric signal upon incidence of a radiation photon, a counter that counts the electric signal from this sensor, and a count value of the counter that is over capacity during image data sampling. When the counter does not become over capacity during data sampling, the operation processing means includes a time counting means for measuring the data sampling time until the time when the capacity is over, and an arithmetic processing means. When the image data is obtained from the count value and the capacity is exceeded, the image data is obtained from the value obtained by dividing the capacity value of the counter by the time value measured by the time measuring means, and the data is output on the screen. An imaging device configured to perform.